This project proposes to synthesize a number of ATP analogs with modified purine and triphosphate moieties. These analogs will be tested to see if they are substrates of myosin containing enzymes. If so, the kinetics of hydrolysis including the pH dependence, the effect of divalent metal ions, the effect of temperature and ionic strength will be determined and compared with ATP. If the analogs are not substrates, then binding and possible inhibition of ATP hydrolysis will be studied and the parameters of the system defined. The analogs will also be studied to determine their effects on the more complex actomyosin and muscle fibril systems in an effort to ascertain the exact substrate requirements for contraction. In particular, analogs capable of covalently labeling myosin, actin or other contractile proteins will be sought. Where appropriate, other ATP splitting enzymes will be tested with these affinity labeling compounds to compare their active sites with myosin and related proteins.